Various products and techniques are available to measure chemicals in water; the cheapest way is to use either dip strips or chemical regent kits. Both these methods require time from the user and some know how. There are some reversible fixed colorimetric sensor pads that can be used permanently fixed in an aquarium but they still require a user to read and compare the colour which is hard under varying light sources, and the results can also be affected by subjective comparisons. Most people test water reactively and interpret one set of results to diagnose what has gone wrong.
Prior art on reversible NH3 and pH sensors can be found in WO2007/115321 and EP1813939.
An alternative to manual tests and interpretation comes at a much higher cost and involves the use of Ion specific electrode probes (ISE). These devices are usually sold as single probes with a hardware solution attached to each sensor. These are expensive and temperamental in operation requiring frequent calibration over time. ISE probes suffer badly from drift as the electricity passing through the electrodes cause biological growth which covers and affects them. Recently optically based probes are becoming more popular in the scientific world as a replacement to ISE probes; they are usually at a higher cost but they offer greater accuracy and robustness. Examples include EP1840566.
We have therefore appreciated the need for an improved optical sensor for detecting chemicals in a fluid, such as water, that does not require a user to interpret colour changes.